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    PLAIN BEARING FAILURE

    8.0 Electrical damage

    Click on photograph to enlarge 
    Electrical arcing damage on the journal of a vertical electric motor
    Main CharacteristicsThis is an unusual type of electric damage, similar in appearance to 'washboarding' in rolling bearings
    CauseThe damage shown in the Photograph occurred on a 4 MW vertical motor on a standby water pump. The motor was run each month for about an hour. This pattern of operation lead to the laying down of wear dust from the carbon brushes that in time caused an explosion that was traced to arcing in the end cover. The damage to the journal was found when the machine was stripped to investigate the explosion. Similar damage was found on other motors in the pumping station that were subject to the same operating regime.
    NoteThe direction of motion in the Photograph is horizontal. Note that most of the lines of marks follow the direction of motion, some are at an angle of about 45°.
    Possible Confusion with
    Other Types of Damage    		 
    CommentNo explanation was found to account for the effect, but it is worth illustrating as an example of electrical damage.